We saw many students playing on the playground most of them girls.A. areB. beingC. were

问题补充：

We saw many students playing on the playground, most of them girls.

A. are

B. being

C. were

D. have been

答案：

A. are

(答案→)B. being

C. were

D. have been

解析：考查独立主格结构。句意：我们看到很多学生在操场上玩，他们中大部分是女生。most of them girls.前缺少连词，可知下文为独立主格结构。现在分词短语表示正在进行的伴随性动作，结合语境可知选B。